1. Field of the Invention
The invention relates to seedbed preparation implements and, more particularly, relates to a disc gang usable, e.g., on a multifunctional seedbed preparation implement and having an adjustable gang angle.
2. Discussion of the Related Art
An increasing number of seedbed preparation implements are configured to till the soil, level it, and/or break up lumps in a single pass so as to minimize the number of passes required to prepare a field for planting. Implements of this general type are sometimes known as “multifunctional seedbed preparation implements.” Multifunctional seedbed implementation implements are gaining popularity because minimizing the number of required passes conserves fuel and also reduces wind and water erosion.
One type of multifunctional seedbed preparation implement is the so-called Combo Mulch Finisher, manufactured, e.g. by Case Corporation. The Combo Mulch Finisher includes a disc harrow having one or more disc gangs, a cultivator located behind the disc harrow, and an optional rotary or tine harrow located behind the cultivator. The three tandem-oriented implement components are configured to partially or completely prepare a seedbed for planting, yet leave a high residue cover for maximum conservation efforts. Specifically, the front disc harrow aggressively cuts and sizes residue ahead of the cultivator and turns the soil to bury some of the residue. The cultivator shatters clods produced by the disc harrow, mixes the clods with the soil, incorporates chemicals, and returns some of the residue to the surface. The rear harrow, if present, reduces clods and levels ridges left by the cultivator. The working depth of the entire implement can be adjusted by raising or lowering the cultivator mainframe relative to the wheels that support it on the ground. In some implements of this type, the working depth of the individual disc gangs of the disc harrow can be independently adjusted by raising and lowering at least a disc-suspension portion of each disc gang relative to the cultivator.
Each disc gang typically includes a plurality of concave circular steel discs with tapered or beveled peripheral edges. The discs, although tending to roll or rotate as they are pulled forward, penetrate into and break up the soil and stalks and other residue lying on the ground. The soil and residue then ride along and across the concave surfaces so as to be turned or inverted. A portion of the residue is buried with this turning, with the percentage of buried residue increasing with the amount of soil turning. The amount of soil turning is determined, in part, by the angle of attack of each disc blade relative to the draft direction, i.e., the direction along which the implement is being pulled along the field. This angle of attack is known as the “gang angle” and is defined as the angle of the discs' gang axis relative to a line extending perpendicularly to the draft direction. Typical gang angles range from 5° to 10°, but other angles are used in some situations.
It is often desirable to adjust the gang angle in order to set or maintain a desired amount of soil turning for, e.g., residue management or tilth management purposes. Residue management comprises controlling a seedbed preparation implement to leave a desired percentage of the seedbed surface covered by crop residue. This percentage typically ranges from about 30% to about 70%, depending on field conditions and other factors. Proper residue management provides several benefits, including:                protecting the soil surface from compaction, crusting, and erosion by absorbing the energy of rainfall on the soil;        building soil organic matter to increase moisture holding capacity and expand soil nutrient pool;        building and strengthening soil aggregates to resist crusting and provide adequate pore space and water permeability;        improving water infiltration;        accelerating soil warming to take full advantage of the growing season; and        creating a soil environment needed for higher yields.        
Soil tilth is a measure of the relationship between the soil, air, water, organic matter, and biological activity. Good soil tilth has approximately 50% mineral soil and organic matter and about 50% pore space. Maintaining good soil tilth provides several advantages, including:                maximizing water and air permeability to reduce ponding, run-off, and erosion;        allowing good early root growth;        increasing air and water exchange from plant food availability;        enabling percolation of excess water deep into the soil; and        enabling roots to penetrate deeper into the soil to provide moisture needed during periods of drought.        
Setting the gang angle at a desired value is one viable method of obtaining desired residue retention and/or tilth characteristics under prevailing soil conditions and operating speeds. It would be beneficial to adjust that angle to obtain different residue retention and/or tilth characteristics under the same operating conditions or to maintain the same residue retention and/or tilth characteristics as soil conditions and/or operating speeds vary from area to area or even from field to field. Hence, incorporating gang angle adjustability into a disc gang of a multifunctional seedbed preparation implement would considerably increase the flexibility and versatility of a disc gang. However, no heretofore known multifunctional seedbed preparation implement employed disc gangs with adjustable gang angles. This lack is believed to result from impracticalities resulting from the ways in which these machines were constructed and operated.
The gang angles of some standalone disc harrows are adjustable, but adjustment is typically either difficult or imprecise. For instance, U.S. Pat. No. 3,080,933 to Kramer, U.S. Pat. No. 4,180,135 to Birkenbach, and U.S. Pat. No. 5,462,123 to Harlan all disclose tandem disc harrows having front and rear sets of disc gangs, each of which includes two disc gangs that have independently adjustable gang angles. Each disc gang of all of these systems includes a rigid frame that is mounted on the mainframe of the disc harrow so as to pivot about a vertical axis. Another portion of the frame is mountable on the mainframe only at a selected one of a plurality of discreet, spaced-apart mount points, usually taking the form of spaced mounting holes in a plate on the disc harrow's mainframe. As a result of this configuration, the gang angle cannot be adjusted “infinitely”, i.e., continuously within the range of gang angle adjustment. It instead can be adjusted only discreetly, with a degree of precision that is limited by the spacing between the mount points. The resultant configuration has relatively low flexibility and versatility. It is also poorly suited for adaptability to disc gangs used in a Combo Mulch Finisher or any other multifunctional seedbed preparation implement.
The need therefore has arisen to provide a multifunctional seedbed preparation implement having disc gangs with adjustable gang angles.
The need has also arisen to provide a disc gang that is usable either on a multifunctional seedbed preparation implement or on a standalone disc harrow and that has infinite gang angle adjust capability, at least over a designated range of gang angle adjustment.